This invention relates to reversible pumps. More particularly, this invention relates to such a pump integrated with a system to efficiently transfer fluid between inflatable bladders in seat cushions by use of the pump and an equalization valve that equalizes pressure between bladders after one bladder has reached its desired maximum inflation and before the pump reverses to begin inflating another bladder.
Although the pump system of this invention has a variety of different applications, its main application is as a system to inflate and deflate sets of bladders in seat cushions. The ability to shift the pressure points on the anatomy of a seated person by inflating and deflating air bladders has important medical, safety and comfort effects. People who are confined to wheel chairs for long periods of time often develop pressure sores on their posteriors. One solution is that presented in U.S. Pat. No. 5,163,737 to Navach et al. in which teaches a contoured cushion with inflatable bladders. The bladders therein are inflated either by motion of the person to shift air between bladders or by an external air compressor with sequenced inflation valves and exhaust valves. This reference contains an excellent description of the medical aspects of pressure ulcers and the preferred locations for bladders and the conformation of the cushion as a whole. As such, this reference is incorporated by reference in its entirety. Nevertheless, the inflation/deflation systems taught therein are not optimal for some applications. The power drain of an air compressor is too much for many electric wheel chairs, and many users either do not have the physical strength to push on the bladders themselves. Also, other users lack feeling in these areas of their bodies and cannot sense when the blood circulation to their pressure points has ceased.
Another solution was later developed that utilized a constant flow turbine air pump with a sequencing valve. This battery-powered pressure supply system was packaged in a separate box and attached to the back of a wheelchair. While effective in clinical settings, it requires too much battery energy, is too heavy, and is too large to be conveniently used in home settings.
Use of cushions with inflatable bladders is not limited to wheel chair applications. Anyone sitting for prolonged periods of time, in a chair can benefit from a cushion with bladders that inflate and deflate to shift the pressure points and stimulate blood circulation. Long haul truck drivers in particular have a need for seats employing such cushions. Tests have shown that such cushions improve their alertness, implying an important safety benefit. Such inflatable seat cushions have existed for some time. However, the pump systems are not particularly efficient. One typical arrangement is that taught in U.S. Pat. No. 4,938,528 to Scott which mentions that reversible pumps can be used to inflate and deflate a bladder but also opines that such pumps are inefficient. This reference does not employ the equalization valve of the present invention. There remains an unmet need in the art for a high efficiency pump system that will transfer fluid between bladders for applications such as these seat cushions, particularly for mobile applications.